Impregnation of absorbent materials



Nov. 5, 1957 .1. l.. MATHERNE ETAL 2,812,271

IMPREGNATION OF' ABSORBENT MATERIALS Filed April 27, 1953 .fase/,A L. ffqmemf [lo wir/Lrg Reid ,1-'win Y IN NTORS HZOPI-fy United States arent O 2,812,271 IMPREGNATION F ABSORBENT MATERIALS Joseph L. Matherne, Roaue County, Tenn., and Lloyd Ewing and Reid Ewing, Milwaukee County, Wis., as-

sguors to McGraw-Edison Company, a corporation of The present invention relates to a method of impregnating absorbent materials, and particularly pertains to the controlled impregnation of fibrous materials that are apt to swell or shrink when subjected to conditions of hydration or dehydration, respectively, in addition to providing an article manufactured by said method.

In the past there has been serious difficulties encountered with the use of impregnated fibrous conduit. This conduit is used for the protection of underground electrical cables and other devices that must be protected from mold, moisture and other damaging influences. One of the grave problems has been the occurrence of internal blistering and structural breakdown that has been found to be due to swelling and/or shrinking of the fibrous materials from which the base structure is fabricated. In many instances these conduits areV imbedded in concrete, which provides a very resistant bond with the external surfaces. If the conduit tends to blister or otherwise deform, the effect will be to block the bore of the tube which will prevent insertion or withdrawal of cables and the like. In addition, the forces provided by blistering have often caused injury to the electrical insulation of the cables. Blistering reduces the protective area and permits entrance of seepage water with consequent deleterious effects.

In the case of fibrous bases for conduits, waste newsprint and paper pulp, or other cellulose materials, are beaten in paper beaters and the resultant stock screened and then pumped to paper cylinder machines where they are formed into wet felts or paper. The wet paper may be wound about a cylindrical or other shaped tube or mandrel to produce a wet conduit of proper thickness. This conduit is dried in kilns to remove the major portion of its moisture content. It is to be noted that the wall thickness of the conduits may range from one-quarter inch to one-half inch, as compared to an internal diameter range of from 2" to 6" on pipes or conduits that are produced in 5 to 8 foot lengths. It will be obvious that these articles provide a vast amount of wall surface compared to the wall thickness, wherein blistering and other structural deformations may deleteriously affect their mechanical strength after a relatively short installation period has transpired.

It is, therefore, an object of the present invention to provide a method and means for controlling the porosity of an impregnated absorbent article by controlling the absolute pressure in the unimpregnated voids during impregnation.

It is another object of the present invention to provide a method and means of impregnating an absorbent article having fibers that are susceptible to swelling and shrinking in the presence of a moist atmosphere, by controlling the absolute pressure during the process of impregnation.

It is a further object of this invention to provide as a new article of manufacture an impregnated absorbent article having a predetermined porosity after impregnation to provide void spaces throughout its impregnated surfaces figure, partly in section, denotes a convenient arrangement for impregnating a fibrous conduit or tube in accordance with the present invention. 4The tubular article 1 is capped or closed at one `end with a plug member Z or similar closure member. The opposite end ofthe tubular article is enclosed by means of a closure or plug member 3 which communicates with the interior of the tube as well as with an evacuating means (not shown). The plug members are preferably tapered to provide a minimum contact with the tubular article 1 in `order to permit optimum access to the wall surface on subsequent impregnation. The impregnant 4 is maintained in a vessel 5,

`which may be heated (not shown), if so desired. The

impregnating bath may consist of any of the usual impregnating materials, such as heat liquified coal tar pitch, bituminous asphalt, or other known impregnants.

It will be obvious that the most thorough impregnation results from the lowest pressures maintained in the wall thickness and bore of a tubular article. However, it is possible to provide porous impregnated articles under the influence of relatively higher pressures. A convenient way of doing this is to evacuate the tube while it is immersed in the impregnant, drawing the vacuum from the interior of the tube. The impregnation will then take place in the direction from the outside wall surface through the wall surface to the Wall interior.

Where it is desired to thoroughly impregnate the tube with a bituminous impregnant, the specific gravity of the finally impregnated article has been found to be 1.28. However, if the absolute pressure in the voids of the wall thickness is kept, for instance, at one atmosphere during impregnation, the specific gravity was found. to be 0.98. By maintaining a pressure of one atmosphere inside the tube with a pressure of two atmospheres absolute on the body of impregnant outside the tube, the finally impregnated tube contained about 25% voids.

A porous tube does not have as high a mechanical strength as a thoroughly impregnated one. However, it has the advantage that when subjected to certain atmospheric conditions, the swelling caused by hydration, or shrinkage caused by dehydration will provide fewer strains in the structure, which might cause internal damage to the tube. This is a characteristic greatly desired in the field of underground electrical construction. The under-` ground tube and conduit is usually installed in relatively damp places. The cellulose fibers from which it is made slowly absorbs water and swells. This has been found to happen even under conditions where pipes have been thoroughly impregnated. Strains are often set up which cause the tube to delaminate and fail structurally. When impregnated under controlled evacuating conditions, such as described above, the cellulose fibers may swell, but the swollen fiber has a place into which it may expand. Thus, internal stresses which may be sufficient to cause rupture of the impregnated article are much less likely to occur. The multiplicity of expansion areas prevent a continuous delamination by localized absorption of strains.

It will be obvious from the above description that controlled impregnation may be successfully accomplished under conditions of increased pressure, if so desired. That is, the invention may be practiced by regulating the relative atmospheric pressures exerted on the outer and inner surface of the article to be impregnated. The convenient manner of accomplishing this has been to draw a vacuum on the interior of the tubular member while permitting the body of impregnant to remain at atmospheric pressure.

We claim:

A process for the controlled impregnation of a fibrous tubular article formed of a plurality of wound paper coextensive therewith, which process comprises maintainf ing a body of impregnant, drying said article to substan- Y tially remove occluded water and water vapor from said article, closing one end of said` bore with a iirst plug member, closing the opposite end of said bore with a second plug member communicating with an evacuating means, immersing said article and plug members in said impregnant for a selected impregnation period, reducing the pressure within said bore through said second plug member to a 1:2 ratio relative to the pressure affecting the exterior of said article, maintaining said pressure ratio throughout said impregnation period Ato provide a substantial impregnation of said article through the said porous wall surfaces and to `provide a predetermined amount of voids in the interstices of said porous brous articles, whereby the bers of said fibrous article may be free to expand and contract without deleteriously affecting said surfaces.

References Cited in the ile of this patent UNITED STATES PATENTS Kirchenbauer June 20, Zavertnik et al. Aug. 1, Miller Sept. 3,V Miller Sept. 3, Hensel Dec. 12, Reid Feb. 27, McDermott .-,,,t,, Aug- 21, Stewart et al May 7, VonLiedtke Aug' 9, Piercy et al Nov. 21, Coggeshall -Apr. 24, Kroft May 22, Ewing Jan. 10, 

